Nanoporous Metal Phosphonate Hybrid Materials as a Novel Platform for Emerging Applications: A Critical Review

Nanoporous metal phosphonates are propelling the rapid development of emerging energy storage, catalysis, environmental intervention, and biology, the performances of which touch many fundamental aspects of portable electronics, convenient transportation, and sustainable energy conversion systems. Recent years have witnessed tremendous research breakthroughs in these fields in terms of the fascinating pore properties, the structural periodicity, and versatile skeletons of porous metal phosphonates. This review presents recent milestones of porous metal phosphonate research, from the diversified synthesis strategies for controllable pore structures, to several important applications including adsorption and separation, energy conversion and storage, heterogeneous catalysis, membrane engineering, and biomaterials. Highlights of porous structure design for metal phosphonates are described throughout the review and the current challenges and perspectives for future research in this field are discussed at the end. The aim is to provide some guidance for the rational preparation of porous metal phosphonate materials and promote further applications to meet the urgent demands in emerging applications.

A Robust Mesoporous Al2 O3 -Based Nanocomposite Catalyst for Abundant NOx Storage with Rational Design of Pt and Ba Species

The nanostructural design of heterogeneous catalysts has often been demanded for assessing synergetic effects, which should be developed further by using high-surface-area porous metal oxide supports. However, such opportunities have been undermined by the poor stability of ordered mesoporous structures. Herein, rational design is demonstrated to obtain nanocomposite catalysts showing improved NO_x storage properties owing to the presence of Ba species over a well-designed mesoporous alumina (Al₂ O₃ ) support. It is found that Ba species are impregnated successfully only after the stabilization of the mesoporous structure by full crystallization of Al₂ O₃ frameworks to the γ-phase, with the formation of Pt nanoparticles coinciding with complete removal of organic components. All the insights during this synthetic procedure are essential for designing high-performance catalysts to purify and recover NO_x molecules, and are applied for designing a variety of cutting-edge mesoporous nanocomposite catalysts.

Further Understanding of the Reactivity Control of Bisphosphonates to a Metal Source for Fabricating Highly Ordered Mesoporous Films

Mesoporous metal organophosphonates having embedded organic functions are a promising platform to hybridize organics and non-siliceous inorganic frameworks in their molecular scale. However, the reactivity between a bisphosphonate and a metal source is dramatically different for their combination and then hampers to construct ordered mesoporous structures even when using amphiphilic organic molecules. By proposing an advanced method to adjust such reactivity, we recently succeeded in fabricating ordered mesoporous aluminum organophosphonate (AOP) films with chemically designable benzene units inside their hybrid frameworks. The reactivity of the organically bridged bisphosphonates has been controlled by utilizing dissimilar reactivities of acid-base pairs like P-OH and P-OEt groups to AlCl₃ . Here, we further prove our reactivity-control concept through the introduction of organic groups, such as those having symmetric thiophene, asymmetric amide, and hydrophilic ether units. Liquid-state ³¹ P NMR measurements further clarified the usefulness of the control of the -OH/ -OEt ratio in the same bisphosphonate molecules for obtaining highly ordered mesostructured AOP films.

Formation of aluminum diphosphonate mesostructures: The effect of aluminum source

Mesostructured aluminum phosphonates (AOP-x) bridging with 1,1'-hydroxyl ethylidene groups, including a lamellar mesostructure (AOP-N) with crystalline framework, a well-ordered 2D-hexagonal mesophase (AOP-Cl), and a particle-packed mesostructure (AOP-S), were simply synthesized in the presence of surfactant cetyltrimethylammonium bromide in the ethanol-water system, by choosing Al(NO₃)₃, AlCl₃ and Al₂(SO₄)₃ as the aluminum source, respectively. The crystallinity, morphology, mesophase, and skeletal structure of the as-prepared materials were characterized by XRD, TEM, SEM, ²⁷Al, ³¹P and ¹³C MAS NMR, and nitrogen sorption techniques. After calcination under N₂ at 350 °C, the calcined AOP-x samples consist of aluminum phosphonate and phosphate, possessing desirable specific surface areas of 116-585 m²/g. The effect of the inorganic counteranions (NO₃^-, Cl^- and SO₄^2-) from the aluminum source on the formation of different AOP-x mesostructures was discussed in terms of their bind strength to the headgroups of the surfactant micelles, suggesting the potential for designed synthesis of non-silica-based mesostructured organic-inorganic hybrid materials.

The effect of the buffer solution on the adsorption and stability of horse heart myoglobin on commercial mesoporous titanium dioxide: a matter of the right choice

Despite the numerous studies on the adsorption of different proteins onto mesoporous titanium dioxide and indications on the important role of buffer solutions in bioactivity, a systematic study on the impact of the buffer on the protein incorporation into porous substrates is still lacking. We here studied the interaction between a commercial mesoporous TiO₂ and three of the most used buffers for protein incorporation, i.e. HEPES, Tris and phosphate buffer. In addition, this paper analyzes the adsorption of horse heart myoglobin (hhMb) onto commercial mesoporous TiO₂ as a model system to test the influence of buffers on the protein incorporation behavior in mesoporous TiO₂. N₂ sorption analysis, FT-IR and TGA/DTG measurements were used to evaluate the interaction between the buffers and the TiO₂ surface, and the effect of such an interaction on hhMb adsorption. Cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) were used to detect changes in the microenvironment surrounding the heme. The three buffers show a completely different interaction with the TiO₂ surface, which drastically affects the adsorption of myoglobin as well as its structure and electrochemical activity. Therefore, special attention is required while choosing the buffer medium to avoid misguided evaluation of protein adsorption on mesoporous TiO₂.

Biocarbon-templated synthesis of porous Ni–Co-O nanocomposites for room-temperature NH3 sensors

Mesoporous nickel–cobalt oxide (Ni–Co-O) nanocomposites were fabricated using a mesoporous biocarbon material (BCM), resulting from hemp stem, as a template.

C-H hydroxylation of phosphonates with oxygen in [bmIm]OH To produce quaternary α-hydroxy phosphonates

A highly efficient and mild [bmIm]OH-catalyzed α-hydroxylation of phosphonates using O2 as the oxygen source is described. The employment of ionic liquid under mild reaction conditions makes this transformation green and practical. Especially, this reaction provided a novel and convenient methodology for the construction of quaternary α-hydroxy phosphonates.

Insights into mesoporous metal phosphonate hybrid materials for catalysis

Mesoporous metal phosphonates have received increasing attention as promising heterogeneous catalysts due to their abundant framework compositions and controllable porosity.

Co2+-loaded periodic mesoporous aluminum phosphonates for efficient modified Fenton catalysis

Periodic mesoporous aluminum phosphonates exhibit high uptake capability for Co²⁺ and thus oxidizing ability in organic contaminant decomposition.

Mesoporous zirconium phosphonate materials as efficient water-tolerable solid acid catalysts

Mesoporous zirconium phosphonate materials were fabricated as efficient water-tolerable solid acid catalysts.

Hollow cobalt phosphonate spherical hybrid as high-efficiency Fenton catalyst

Organic-inorganic hybrid of cobalt phosphonate hollow nanostructured spheres were prepared in a water-ethanol system through a mild hydrothermal process in the absence of any templates using diethylenetriamine penta(methylene phosphonic acid) as bridging molecule. SEM, TEM and N2 sorption characterization confirmed a hollow spherical micromorphology with well-defined porosity. The structure and chemical states of the hybrid materials were investigated by FT-IR, XPS and thermogravimetric analysis, revealing the homogeneous integrity of inorganic and organic units inside the network. As a heterogeneous catalyst, hollow cobalt phosphonate material exhibited considerable catalytic oxidizing decomposition of methylene blue with sulfate radicals as compared to cobalt phosphonate nanoparticles synthesized in single water system, which could be attributed to enhanced mass transfer and high surface area for the hollow material. Some operational parameters, including pH and reaction temperature, were found to influence the oxidation process. The present results suggest that cobalt phosphonate material can perform as an efficient heterogeneous catalyst for the degradation of organic contaminants, providing insights into the rational design and development of alternative catalysts for wastewater treatment.

Mesoporous cerium phosphonate nanostructured hybrid spheres as label-free Hg²⁺ fluorescent probes

Porous phosphonate-based organic-inorganic hybrid materials have been shown to have novel and amazing physicochemical properties due to the integration of superiorities from both inorganic components and organic moieties. Herein, mesoporous cerium phosphonate nanostructured hybrid spheres are prepared with the assistance of cationic surfactant cetyltrimethylammonium bromide while using ethylene diamine tetra(methylene phosphonic acid) as the coupling molecule. The resulting hybrid is constructed from the cerium phosphonate nanoparticles, accompanied by high specific surface area of 455 m(2) g(-1). The uniform incorporation of rare-earth element cerium and organophosphonic functionalities endows mesoporous cerium phosphonate with excellent fluorescence properties for the development of an optical sensor for selective Hg(2+) detection on the basis of the fluorescence-quenching mechanism. The signal response of mesoporous cerium phosphonate against the Hg(2+) concentration is linear over the range from 0.05 to 1.5 μmol L(-1), giving a limit of detection of 16 nmol L(-1) (at a signal-to-noise ratio of 3). Most of the common physiologically relevant cations and anions did not interfere with the detection of Hg(2+). This label-free system provides a promising platform for further use in bioimaging and biomedical fields.

Hollow manganese phosphonate microspheres with hierarchical porosity for efficient adsorption and separation

Hollow manganese phosphonate microspheres of an inorganic-organic hybrid with hierarchically porous shells were prepared through a template-free hydrothermal method using ethylene diamine tetra(methylene phosphonic acid) as the coupling molecule. The hollow structures with hierarchical porosity were confirmed by SEM, TEM and N2 sorption. FT-IR, XPS and TG-DSC measurements revealed that the organophosphonate linkers were homogeneously incorporated into the hybrid framework. The hierarchical manganese phosphonates could be used as efficient adsorbents for the removal of copper ions, showing fast binding kinetics due to the well-structured porosity. The adsorption process follows pseudo-second order reaction kinetics, as well as Langmuir isotherm, indicating that Cu(2+) was monolayer adsorbed on the hybrid by chemical complexation. Furthermore, the synthesized manganese phosphonates with peculiar porosity exhibited excellent size selectivity for protein adsorption in a complex solution, presenting the promising potential as candidates for biomaterials.

Encapsulation of large dye molecules in hierarchically superstructured metal–organic frameworks

A perturbation assisted nanofusion technique to construct hierarchically superstructured MOFs was reported. In particular, the mesopores in the MOF structure enabled the confinement of large dye species, resulting in fluorescent dye@MOF composite materials.

Synthesis of amorphous porous zirconium phosphonate materials: tuneable from micropore to mesopore sizes

Amorphous super-microporous zirconium phosphonates with tunable pore size distributions were hydrothermally synthesized in a CTAB–H₂O–ethanol system by controlling the aging time.

Metal phosphonate hybrid materials: from densely layered to hierarchically nanoporous structures

Inorganic–organic metal phosphonate hybrid materials with great diversity in structure and properties exhibit application potential in various fields.